1. Field of the Invention
The present invention is related to a color solid imaging device comprising a color separation filter, and particularly to a frame transfer type CCD solid-state color imaging device.
2. Description of the Prior Art
In a single-layer color imaging device, a color separation filter with a mosaic, stripe or other pattern is mounted on the light receptor surface of the CCD solid-state color imaging device in the imaging device, and the elements on the receptor surface are made to correspond to specific color components. When a mosaic-pattern color separation filter is used, horizontal resolution is greater than when a striped-pattern color separation filter is used, but a problem exists in that the processing of video signal obtained from the CCD becomes complex.
FIG. 1 is a diagrammatic view showing the prior art frame transfer type CCD solid-state color imaging device to which is mounted a mosaic color separation filter.
On the receptor surface of the CCD, multiple channel areas 1 are provided extending in the vertical direction separated by channel separation areas 2 therebetween. A two-layer structure transfer electrodes 3 and 4 is formed perpendicular to the multiple channel areas 1 through an insulation layer. In addition, the upper transfer electrode 4 is formed on channel separation areas 2 with a narrow width to improve transfer efficiency. To these transfer electrodes 3 and 4 is applied, for example, a four-phase transfer clock, and the information charge produced in the multiple channel areas 1 is transferred along the multiple channel areas 1.
The mosaic color separation filter 10 mounted on the receptor surface is divided according to the pixels of the receptor surface so that yellow (Ye), cyan (Cy), green (G), and white (W) filters is applied to each divided area in a specific order. The elements on the receptor surface are separated in the vertical direction by the channel separation areas 2, and are separated in the horizontal direction by the potential barrier formed by the transfer electrodes 3 and 4. Specifically, the area near the end of the transfer electrodes 3 and 4 becomes the boundary of each element, and the width of one transfer electrode 3 and 4 is equivalent to one element. Therefore, the color separation filter 10 is divided in the vertical direction along the channel separation areas 2, and is divided in the horizontal direction along the edge of the transfer electrodes 3 and 4.
In a CCD of this type, two elements in the vertical direction are normally read simultaneously, and interlace drive is used to invert the combinations of elements in each field to improve resolution. Specifically, in odd fields, elements in line n and line n+1 are read simultaneously, and in even fields elements in line n-1 and line n are read simultaneously. The brightness signal and the chrominance signal are then obtained from the sum and difference, respectively, of the signals read from the CCD in the horizontal direction. For example, when the colors are arranged as shown in FIG. 1, the chrominance components for W and Ye, G and Cy are mixed and read in the odd fields, and the brightness signal is obtained from (W+Ye)+(G+Cy), and the chrominance signal is obtained from (W+Ye)-(G+Cy). Similarly, in the even fields, the color components for Ye and W, Cy and G are mixed and read, and the brightness signal is obtained from (Ye+W) +(Cy+G), and the chrominance signal is obtained from (Ye+W)-(Cy+G). Thus, because W=R+G+B, Ye=R+G, and Cy=G+B (where R= red, B=blue), the brightness signal becomes 2R+4G+2B combining the odd and even fields. Furthermore, the chrominance signal is 2R with both fields. If Ye and Cy are inserted, the chrominance signal becomes 2B.
However, the receptor surface of a frame transfer CCD as shown in FIG. 1 has insufficient element separation in the horizontal direction compared with an interline transfer-type CCD, which also has channel separation areas in the horizontal direction, because the element separation in the horizontal direction is formed by the potential barrier formed by the transfer electrodes 3 and 4. Thus, there is the possibility of part of the information charge for each element leaking to the element adjacent in the vertical direction. For example, in the G element as shown in FIG. 2, the information charge of one part (g) of the G element leaks out, and the information charge of one part (y) of the Y element leaks in. Such information charge leakage is produced in each element, and error in the information charge of each element occurs. If the quantity of this information charge leakage is expressed as .DELTA.Ye, .DELTA.Cy, .DELTA.G, and .DELTA.W, the brightness signal and chrominance signal in even fields become (Ye+W-.DELTA.Ye+.DELTA.Cy)+(Cy+G -.DELTA.Cy+.DELTA.Ye), and (Ye+W-.DELTA.Ye+.DELTA.Cy)-(Cy+G -.DELTA.Cy+.DELTA.Ye), respectively, and can be calculated as 2R+4G+2B and 2R-2.DELTA.Ye+2.DELTA.Cy. Also, the brightness signal and 2R-2.DELTA.Cy. also, the brightness signal and chrominance signal in the odd fields become (W+Ye-.DELTA.W+.DELTA.W)+(G+Cy-.DELTA.G+.DELTA.G), and (W+Ye-.DELTA.W+.DELTA.W) -(G+Cy -.DELTA.G+.DELTA.G), respectively, and can be calculated as 2R+4G +2B and 2R. Therefore, the brightness signal is the same as in that case in which information charge leakage is not considered, but an error of (-2.DELTA.Ye+2.DELTA.Cy) occurs in the chrominance signal. Thus, the video signal contains error in the color component in each field, resulting in flicker in the playback image.
One countermeasure to this flicker is to provide a color separation filter configured according to the range of expected information charge leakage, but it is extremely difficult to actually provide a filter so formed for color separation because the configuration of each separation area in the color separation filter becomes complex. Furthermore, while it has been proposed, for example in Japanese Patent Publication (examined) No. 60-41872, to form a light barrier range of a constant width from aluminum, etc., at the boundary area of each separation area, this is not suited to a frame transfer CCD wherein there are no channel separation areas in the horizontal direction, and such problems result in the reduction of the light sensitivity, and the difficulty in achieving complete light blocking.